(1) Field of the Invention
The present invention relates to an ellipsometer using an expaed beam, and more particularly to an ellipsometer which can measure the thickness and a refractive index of a film such as an oxide film on a semiconductor substrate at a high speed and with a low error rate.
(2) Description of the Related Art
As a prior art of an ellipsometer, an automatic ellipsometer invented by Frederic H. Dill et. al, described in U.S. Pat. No. 3,880,524 issued on Apr. 29, 1975, is known. In this prior art, to measure one point on a sample, the state of polarization of light is measured by rotating, mechanically or electrically, and azimuthal angle of an analyzer to detect the total amount of transmitted light, thereby the thickness and the refractive index of he sample are measured.
The rotation of the analyzer from zero degree to 360 degree, however, takes a long time of, for example two to three seconds. In addition, during the rotation, if noises are added to the detected light or if the light intensity fluctuates, the detected result is not correct. Further, since only one point of the sample is detected by one measurement, it takes a very long time to measure the whole surface of the sample.
To speed up the measurement, another prior art is known (Japanese Patent Application No. 62-184250) in which a beam splitter is used to divide a reflected light into three, and three light detectors having different azimuthal angles to each other are used to transmit the divided three reflected light beams, to obtain the state of the polarization of the reflected light by measuring the transmitted light amounts.
This prior art also has a disadvantage of low speed detection because the light beam is incident on only one point on the surface of the sample at one measurement.